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(Tin phosphide)

The analysis of phosphor-tin, which is used especially for the preparation
of phosphor-bronzes, includes :

1.  Determination of the Phosphorus.1—The alloy is treated with
hydrochloric acid and the phosphorus thus liberated as hydrogen phosphide,
which is oxidised with bromine water and determined as phosphoric acid.

Apparatus. A flask of about 500 c.c. capacity furnished with a stopper
through which pass (i) a tapped funnel for the introduction of the hydro-
chloric acid and (2) two tubes bent at right angles, one reaching almost
to the bottom of the vessel and serving for the introduction of a stream
of carbon dioxide into the apparatus, and the other to collect the gas evolved
during the reaction. The latter tube communicates with three absorption
bottles, two containing bromine water and a small quantity of bromine
(a layer some millimetres deep) and the third bromine water alone.

Procedure. 2-5 grams of the alloy in small fragments are introduced
into the flask and the latter stoppered and connected with the washing
bottles, a current of carbon dioxide being passed for about five minutes to
expel the air. From 50 to 100 c.c. of concentrated hydrochloric acid are
then added, little by little, and when the attack is complete the liquid is
heated to boiling, and a current of carbon dioxide again passed to drive
out the products of the reaction. The contents of the three bottles are
washed into a beaker, the excess of bromine eliminated by boiling and the
phosphoric acid precipitated either (i) as magnesium ammonium phosphate
which, after standing, is filtered off, dried, ignited strongly and weighed:
Mg2P207 x 0-2787 = P,2 or (2) with ammonium molybdate (see Iron, 4).

2.  Determination  of the  Tin.—The hydrochloric  acid solution is
collected in a 500 c.c. measuring flask and made up to volume.   An aliquot
part, corresponding with 0-5-0-75 gram of the sample, is rendered alkaline
with ammonia, the precipitate redissolved by addition of a little oxalic acid
and the liquid boiled for a short time with 25 c.c. of hydrochloric acid, 25
grams of ammonium oxalate and a few drops of hydrogen peroxide, made
up to about 250 c.c. and electrolysed at 40-50° to determine the tin (see
Electrolytic Determination of Tin in Ordinary Bronzes).

* *

Commercial pliosphor-ti.ii or tin phosphide usually contains about 4% of
phosphorus. The brand marked N.o contains about 5% P and N.I, 2-5%.
Other products, however, contain only i% or even less.

1  W. Gemmell and S. L. Archbutt, Joiirn. Sac. Chew. Industry, 1908, XXVII, p.

2  If the sample contains arsenic, magnesium ammonium arsenate is precipitated
with the magnesium ammonium phosphate.    In this case the weighed precipitate is
redissolved in hydrochloric acid, the solution reduced with sulphur dioxide and the
arsenic precipitated with hydrogen sulphide,

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